DE 38 23 655 A1 has already disclosed a supporting and/or conveying roll, which substantially consists of a roll core and a roll sleeve which can be screwed into one another, for conveying hot metal strands in a continuous casting installation. A build-up weld is applied to the roll sleeve, the welding parameters for carrying out said build-up welding being selected such that joint welding between the core and sleeve is carried out at the same time as the protective build-up is welded onto the outer lateral surface of the roll sleeve. The build-up weld is formed by weld beads which lie closely adjacent to one another in the axial direction of the supporting roll or in the form of a helical line along the lateral surface of the supporting roll. This provides a wear-resistant surface and a solid join between the sleeve and core.
DE 32 23 908 A1 discloses a strand guide roll, the roll body of which is provided with a build-up weld. The build-up weld comprises a multiplicity of weld beads, which are arranged closely adjacent to one another and are applied in a wave-like manner in the circumferential direction of the roll body. The build-up weld is reworked in order to obtain a smooth, cylindrical surface free from cracks. Information relating to the chemical composition of the base material and of the material of the wearing layer welded on, with a view to optimizing the material properties of the strand guide roll, cannot be gathered from this document.
U.S. Pat. No. 4,532,978 A discloses a conveying roll for hot metal pieces, having an outer surface layer produced by build-up welding, by thermal spraying or by shrink fitting, wherein this outer surface layer is formed from a ferritic steel containing less than 0.1% C, 10.0-14.0% Cr and 0.4-1.0% Nb, remainder iron and manufacturing-related impurities. Improved resistance of the surface layer of a conveying roll to corrosion and oxidation and a reduced susceptibility to cracking are achieved by the combination of the alloy components Cr and Nb. More specific information relating to the structure of the outer surface layer formed by build-up welding cannot be gathered from this document.
Build-up welds are generally characterized by the application of a firmly adhering layer to a component surface via the flow of melt. This layer serves not only for producing a wear-resistant surface or for repairing the latter after it has been used for a specific time, but also primarily for reinforcing (protection against wear), cladding (protection against corrosion) and buffering (formation of interlayers) component surfaces.
During build-up welding, the component base body serves as the carrier with sufficiently elastic properties, while the coating, as the functional surface, should protect the component against damage caused by severe loading, including corrosion, wear and/or temperature. Build-up welding combines advantages, such as low dependence on the component geometry, good adhesion between the carrier material and the coating, dense layers and good conduction of heat by the build-up weld into the component. Considerable economic losses arising from a major outlay on maintenance are presently caused by the abrasive and erosive wear on such components, especially on continuous casting rolls of a continuous casting installation.
By way of example, in order to ensure that the service life required for strand guide rolls is achieved in respect of surface wear, which is currently usually about 300 000 tons of metal strand produced in the inlet region of the strand guide (the region following the mold) or 5 million tons in the outlet region from the strand guide, a build-up weld according to the prior art has to have the following properties:                a rust-free build-up weld with a martensitic microstructure,        a hardness of 44-50 HRC,        a high level of resistance to corrosion of the weld layer as a result of an alloy component of at least 12.5% Cr,        heat checking resistance,        the lowest possible delta ferrite content of max. 10%. A delta ferrite content of 0% would be ideal for ensuring a high level of resistance to intercrystalline corrosion. For reasons related to materials and welding, this can only be achieved with difficulty. In practice, a delta ferrite content of up to 10% is therefore acceptable.        
These properties should be present at the functional surface close to the surface in a sufficient layer thickness of the build-up weld applied, so that the surface can still be reworked to a high quality once a permissible wear limit has been reached, particularly without the roll shell being damaged or weakened in the region of the base material.
The microstructure formation and quality of this functional surface close to the surface, which is produced by build-up welding, are dependent on the quality of the base material of the roll shell, on the quality of the weld filler and possibly on the build-up welding operation itself. During the welding operation, the molten base material and the weld filler melting away from the welding wire are mixed, which is referred to as dilution. The obtained dilution of the weld filler with the base material is greatly influenced by a spread in material and welding parameters, which is unavoidable in practice. However, the dilution process essentially determines whether the above requirements made on the build-up weld are met.
In order to obtain sufficiently large wearing layers with invariable material properties, it is already known, for example from JP 10-314938 A2, to carry out multi-layer welds. The problem relating to dilution and thus different material properties therefore prominently arises exclusively in the first layer of the build-up weld. This problem no longer arises in the second layer and in the further layers of the build-up weld. However, the time taken to carry out the build-up weld and the amount of energy which the welding unit needs to consume increase significantly according to the number of weld layers.
JP 11-000747 A2 discloses a supporting roll having a single-layer build-up weld, in which only tips of the weld beads are ground down in a subsequent machining operation, this producing a cylindrical lateral surface which, however, has a functional surface which bears the hot conveyed material only in subregions. That surface of the weld beads which is not machined increases the risk of crack formation as a result of nonuniform loading phenomena and nonuniform transfer of heat from the hot conveyed material into the supporting roll. Appropriate information relating to the quality of the build-up weld, in particular relating to the uniformity of the material properties in the build-up weld and the composition of the weld filler, cannot be found in JP 11-000747 A2.